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1. Field of the Invention
This invention relates generally to excavating tools, and more particularly to earth-drilling augers used for boring through particulate material beneath a surface structure, such as a sidewalk or a foundation.
2. Description of the Related Art
Forming a hole in particulate material, such as soil or sand, under a surface structure is usually effected by a screw-like tool called an auger, which progressively bores or drills into the material. The typical auger has a cutting blade at the distal end of a helical flight that is mounted to an axle. The axle extends longitudinally away from the user, or a rotatable machine, and defines an axis of rotation for the auger. The user rotates the auger, either by hand, or more preferably by the machine. As the auger progressively forms the hole, additional sections of helically flighted axles can be coupled to the auger.
Some prior art augers and drilling tools that are designed for drilling into compacted earth, such as clay, combine pressurized air and working fluid with the auger for continuously loosening debris from the hole. The fluid and debris are channeled into an escape route sub-assembly system, which is typically a longitudinal hole through the axle. In this way, the hole is regularly flushed and kept relatively clean to enable the inner surface of the hole to be dissociated by the drilling action. However, such prior art drilling tools are bulky and awkward due to the attached pneumatic and hydraulic hoses, so they are difficult to maneuver and operate, especially when they are used in narrow spaces. In addition, the escape route sub-assembly system can become clogged with debris, which can damage the tool and delay the overall progress of an operation. Also, fluid can leak from the escape route and soak the surrounding earth, and surface structures can be damaged or lose support from that earth.
Some augers have been made with various types of fasteners for linking flighted modular sections together in series in order to bore a hole to a certain depth. Augers have also been formed with various cutting blades designed for enhancing the performance of the auger. For example, augers have been designed with a tip attached to a leading end of the auger in position for orienting the tip for directional drilling. Still other types of augers have been designed to be compact and portable in order to be transported and used to drill a hole in ice for ice fishing.
A more significant design in the prior art augers involves a limitation to the distance that a helical flight extends along an axle. For example, U.S. Pat. No. 2,221,680 to Parrish teaches an auger having a discontinuous flight attached to the outer surface of the drilling axle. Sections of the flight have been removed from the drilling stem in order to reduce friction that is generated by the rotating land, which is the peripheral edge of the flight, contacting the newly formed sidewall of the hole. This auger more efficiently bores holes, because the frictional force resisting the rotation of the auger is reduced along the auger.
The prior art augers are deficient in significant aspects. For example, the prior art augers are almost always made of an electrically conductive material and utilized near active electrical wires, such as around a dwelling foundation. If a buried wire is broken by the auger, electricity may reach the user by conduction through the auger.
Another significant deficiency is that the prior art augers are difficult to repair. A rotating auger typically encounters resistance from gravel, tree roots, rocks, and compact soils. A counterforce from these obstructions on the flight produces torque that may damage the auger, because the leading end of the auger will have ceased or diminished rotation relative to the proximate end, which still has inertia and torque applied by the power source. Once damaged, the typical prior art augers are usually irreparable without significant rebuilding of the working parts. The connector joints in many prior art augers are relatively elaborate structures having concentric interlocking cylindrical parts combined with cross linking fasteners such as nuts, bolts, and screws. The prior art augers would have to undergo extensive rebuilding in a machine shop instead of at the site where the operation is taking place, thereby delaying the hole-forming operation until the auger is repaired or replaced.
Another significant problem with prior art augers concerns their performance during the hole-forming operation. While the flight is rotating in the hole, contact between the cutting blade at the leading end of the flight and the soil is made within the hole. Usually the cutting blade encounters obstructions, such as rocks and tree roots, which resist the rotational force of the cutting blade. When the cutting blade strikes the obstruction, the obstruction usually remains lodged, becoming a fulcrum that rotates the auger within the hole around the obstruction, thereby causing the auger to pivot on the obstruction. As a result, the auger becomes angled in the hole, and the flight cuts into the sides of the hole causing the hole to become oddly shaped.
Another problem is that the prior art augers lack a structural means for maintaining alignment and steadiness of the auger for the entire duration of the hole-forming operation. Once the hole has been formed to a certain depth, the resistance imposed on the auger by the sides of the hole is diminished along the length of the auger. The resistance is at the leading end of the auger, which is in contact with the soil in the hole. The opposite end of the auger at or near the outside of the hole often wobbles in an elliptical or otherwise eccentric pattern if the axis of the auger is not held in a perfectly coaxial relation to the sidewall of the hole. A significant force must be applied on the auger in order to overcome the tendency of the auger to wobble.
The prior art augers are not completely satisfactory for hole-forming operations, especially where the hole is to be substantially horizontal. An auger with structures for overcoming the deficiencies that have been described is needed.
The invention is a tool for boring. The tool has a first shaft for drivingly linking at a first end to a portable machine that rotates, such as a drill. The first shaft defines a longitudinal axis of rotation when the machine rotates the tool.
A second shaft is drivingly linked to the first shaft. The second shaft has a fastener to which a modular auger section can be drivingly linked. A cylindrical collar is mounted radially outwardly of the second shaft and the fastener. An electrical insulator is interposed between the first and second shafts for electrically insulating the shafts from each other. A shear pin is drivingly linked to the shafts for unlinking the shafts upon the application of a predetermined amount of relative torque to the shafts.
Preferably, one or more auger tips and intermediate auger sections are mounted to the tool to form holes of various lengths and/or depths.